Ferromagnetic cores and method



v Feb. '16, 1960 c. J; ESVELD T AL 2,925,389

, FERROMAGNE'IIC 'CORES AND METHOD Filed Bag. 20, 1954 INVENTORSCORNELIS JACOBUS ESVELDT EVERT WILLEM GORTER AGENT U te s te Pa w2,925,389 .f FERROMAGNETIC CORES AND NIETHOD Cornelis Jacobus Esveldtand Evert Willem'Gorter, Em-

masingel, Eindhoven, Netherlands assignors by mesne assignments, toNorth AmericanPhilips vCompany,:

v Inc., New York, N.Y; a corporation of Delaware:

Application December 20, 1954; Serial'No. 476,530 4 (Cl. 252 -62.5)

. Magnetic cores" having a nearly rectangularihysteresisz loop are ofimportance for a variety of uses; Cores of.

kind are used inter alia for so-called ;.magnetic memories (see forexample W. N. Rapian, Broceedings,

. tain (Rumb ,a'gai g e;

The jquotient t-i/m'ul v ram) H g 5, isa'function' of the appliedmaximum field strength It has been found that this quotient'has amaximum at a definite value of H wn1eh usually is only slightlydifferent from the coercive force H This maximum value of thequotientisdudicated by the symbqllm lm Themeasurements'gof B63 5 andfBballistic, galvanometeri: Heifefalsojas measuiing I'objects' use isvmadeof annular magnetic cores of constant'cross section. of themagneticmaterial throughout the .circum ci u e 9 the -r usf ftaugularahysteresis loop highfrequencyl altefnating-eurof ;the;I.R.E.,April 1952, pages 475 to 478,.andlD; R;

Brown and E. Albers schoenberg, Electronics, April '20 1953, pages 146to 149). Such magnetic memories are i used inter alia in calculating:machines and automatic pilots. An an alternative, these cores are used'inmag V netic switches; v The extent to whichthe approaches torectangularity can be quantitatively expressed in various manners; Ausual fneasure is, for example, the' quotient i I Be! In explanation ofthe signification of the said quotient we refer to Fig. 1, which is-adiagram of part of a saturation magnetisation curve. In thislfigure Brepresents the remanent induction whilst-B representsthat induction atwhich the hysteresis loop is precisely closed; In

practice it frequently is diflicultto measure B .with a high degree ofaccuracy; However, an approximately correct value ofB is readily found"by takingth'e' mean value of the inductions after partial magnetisationand partial demagnetisation respectively (with intervening saturation),both inductions being measured at the same constant cross-section of theferromagnetic material throughout the circumference of the ring andhaving an external diameter which at a maximum is 1.6 times the internaldiameter.

The extent to which the shape of the hysteresis loop approaches torectangularity may also be expressed by means of the so-calledsquareness ratio (129 For the meaning of this quantity we refer tothe-above mentioned literature' For the sake of completeness a shortexplanation follows with reference tolFig. Ziwhich 4 is also a diagramof part of a magnetisatloncurv'e re"- lating to a case wheredemagnetisationwas started before magnetic saturation was reached. Thequantity (R )m.x iS 35 I shape of the hysteresis loop rents .are.usually. concernedl aiid consequently.it is-Lof importance to' reducethefoe'cur'rence :of eddy currents a to a When ferromagnetic alloys areused this may be efiected to a certain extent'by building up themagneticeore from= very thinlayers "of the magnetic material insulatedfrom one anotherif-H owever in many cases it is very 'difficult to-build up coresjhaving a? nearlyrectangular hysteresis loop from thesethin layers. Consequently, at these high frequencies it is of'advantagefand at" even higherfr'quencies it is necessary.to'I-usef magneticallysoft ferric' 'oxide containing materials of spinel structure, for thesematerials already have a very slight electric..conductivity per se.

Forthe usability of; the magnetiecores concerned-as magnetic memoriesand m'agnetic switches it is also es sential that the coercive force issmall (preferably; not

more than 10 oersted and; even lower than 5 oersted) since otherwise,the electromagnetic losses ,are excessive.

According to the 'invention' it has been found that magneticcores''haVing a nearly rectangularhysteresis loop such that the cond ition rfis satisfied, H being less than oersted, are obtainable bymanufacturing them from a material which at least substantially'consists of at least one compound of the formula Ni,Mg Fe O where "x'-=0.20.9, which" "compoundsare producedby heating a'mixture of com'rnay be represented by the formula:

pounds of'nickel, of magnesium" and of iron in the' desired weight ratiotoia temperature of from 1375 to 1475 .-C. in agas atmosphere withaproportio'n of oxygen exceeding 50 percent by volume. r 7 It ispossible to replace a small part of the nickel or magnesium respectivelyby zinc in the compounds of the said composition in so far as they havea comparatively high content of nickelras compared with the magnesiumcontent while maintaining the above-described favourable properties. Thecompounds thus obtained .The compounds containing zinc (which areproduced gfin a manner exactly analogous to that described with respectto those containing no zinc are 1- distinguished i fro,m thosecontainingno zinc by a considerably smaller v "coercive force. As' iswell known, a small coercive force 7 is of advantage inthe usesconcerned since it results in a saving in electric energy.

7 Example A mixture of magnesium carbonate, nickel carbonate, iron oxideand, as the case may be, zinc oxide is ground hayin aalexte fmlldameter. "which at a maximum s 1.6 times the internal diameter;

When using ferromagnetic mateiials having afnea'rly refc-" rer-ficmeigutin absolute alcohol or anhyd'rous benzene and" subsequently pre -fired"at 900 C; in air for one hour. After cooling the reaction product isagain .ground in absolute alcohol for a periodoftime, of, say, 2 hours.Thereupon it. is compressed" to form a ring and this ring isheateniizat-iapproximately 1450" C. in oxy en.

, Thesubjoincd. table-provides. a survey of; the values. of. thequotient. i

il-r or the sqnareness ratio (RQimmi dofthe coercive force H, of themagneticeoresqhavin'g a; composition coming.

within the scope of the present invention; "can osinon g. Raj H Kim. p85 l? 'Niu as ga Niels. 02-8 2.95 N101 ,osi 3:25 m 0'75 3.75 V N ozr 0.82. 2 6; .0,7 2.0.

What is claimed is:

1. A method of manufacturing a ferromagnetic ferrite;

having a substantially square hysteresis loop comprising 1 the steps,forming; a; finelwdivided. mixture: of. nickel, magnesium andironoxidesainproportions corresponding,

said mixture of oxides at a? temperature of about; 13:75 to 1475 C. inatmosphere containing. more: than 5.0%

by volume of oxygen to fornra; ferromagnetic-ferrite.

having; said; composition; said ferrite having:v a: coercive force CH3);less. than4 oersted. andi-fulfil'lingt-at; leastrone. of the followingconditions:

1o) Bit/Ban cs ima' w. '(III (119 notlessthan' 0.6.

having a substantially square hysteresisz loop comprising the steps,forming a finely-divided mixture of nickel,

magnesium, zinc, and. iron oxides in proportion corresponding to acomposition having the formula:

' 8(1-e-.u). yF aQ4 in which x'is between. about 0.6 and 0.8, -y-isbetween 2. A method of manufacturing a. ferromagnetic ferrite;

about 0.1 and 0.3 and x+y= is between. about 0.7 and 0.9,.

and heating; said mixture of oxides: to: a temperature; ofabout. 1375 to1475 in; amatmosphere containmg;

more than; by volume; of oxygen to; form. a ferrite having. saidcompositidnysaid.ferrite havingra coercive.

my as awk -gag: A g g r force (H less than 4'oersted and fulfilling atleast 'on'eof'the following conditions:

(a) B,./B not less than 0.7,

(b) (R not less than 0.6.

3. A ferromagnetic ferrite having a substantially square hysteresis loopformed by firing at a temperature of about 137 5 to 1475 C. in anatmosphere containing more than 50% by volume of oxygen a finely-dividedmixture of nickel, magnesiumand iron oxides in; proportionscorresponding to the formula: Ni Mg Fe O inwhich a is between about 0.2and 0.8, said ferrite having a coercive force (H less than 4 oersted andfulfilling, at least one of the following conditions:

(a.) v B /B not less than 0.7,

(b) (R not less than 0.6.

4. A a ferromagnetic ferrite having a substantially square hysteresisloop formed'by firing atfa temperature of about 1375 C. to 1475 C. in anatmosphere containing more than 50% by volume of'oxy'glen afinelydivided mixture of nickel, magnesium, zinc and iron oxides inproportions corresponding to the formula:

in which x is betweenv about 0.6 and 0.8, y is between 0.1and 0.3, andx+y is between 0.7 and 0.9, said ferrite; having a coercive force (H) ofnot more than 4 oerste'd and-fulfilling at least one of the followingconditions! Philips Technical Review, vol. '16, No. 2, 58, August 1954'.r J. of the Institute of Electrical Engineers, Japan, November 1957, p.7; June 1939,.p. 281.

Harvey et'al.: R.C.A. Review, vol. )6, p. 346 '(publica-. tions in Div.64'). Physica, vol. 3', No. 6, June 193.6, pages 481 482. ComptesRendus, Acadmie des. Sciences, vol; 2.09.

pages 49- (1939), pages 164-167.

UNITED STATES PATENT OFFICE .CERTIFICATE OF CORRECTION t Patent No, 2925 389 February 16, 1960 Cornelis Jacobus. E-sveldt et a1.

- It is hereby certified that error appears in the above n'umberedpatent requiring correction and that the said be'tters Patent shouldread as corrected below.

In the heading to the printed specification between lines 7 and 8,insert Claims priority, application Netherlands December 21, 1953 column1, line 23, for "An", first occurrence 7 read As line 54, for "code"read core Signed and sealed this 4th day of October 1960.

(SEAL) Attest:

KARL H. AXLINE Attesting Officer ROBERT c. wA'rsou Comnissioner ofPatents

3. A FERROMAGNETIC FERRITE HAVING A SUBSTANTIALLY SQUARE HYSTERESIS LOOPFORMED BY FIRING AT A TEMPERATURE OF ABOUT 1375* TO 1475*C. IN ANATMOSPHERE CONTAINING MORE THAN 50% BY VOLUME OF OXYGEN A FINELY-DIVIDEDMIXTURE OF NICKEL, MAGNESIUM AND IRON OXIDES IN PROPORTIONSCORRESPONDING TO THE FORMULA: NIXMG(1-X)FE2O4, IN WHICH X IS BETWEENABOUT 0.2 AND 0.8, SAID FERRITE HAVING A COERCIVE FORCE (HC) LESS THAN 4OERSTED AND FULFILLING AT LEAST ONE OF THE FOLLOWING CONDITIONS: (A)BR/BCL NOT LESS THAN 0.7, (B) (RS)MAX NOT LESS THAN 0.6.